Footwear tannery: 200 m³/day DAF pretreatment case
A footwear-leather producer needed to treat mixed tannery wastewater before discharge to a downstream municipal treatment plant. The published installation record is anonymised here: location, operator and supplier names are deliberately omitted. The technical duty, treatment sequence and reported results are retained.
At 200 m³/day, chemical conditioning followed by a high-solids DAF removed more than 90% of suspended solids, more than 67% of COD and BOD₅, and more than 98% of trivalent chromium. The process also produced dewatered sludge at 35% dry matter.
What the DAF had to treat
The feed was mixed wastewater from a footwear tanning process, rather than a segregated chrome-recovery stream. That distinction matters: the DAF was a robust primary-treatment stage, not a substitute for chrome recovery or downstream biological treatment.
| Parameter | Reported influent | Reported DAF result |
|---|---|---|
| pH | 3 | Corrected before flotation |
| Total suspended solids | 1,000 mg/L | >90% removal; calculated outlet upper bound <100 mg/L |
| COD | 3,000 mg/L | >67% removal; calculated outlet upper bound <990 mg/L |
| BOD₅ | 1,500 mg/L | >67% removal; calculated outlet upper bound <495 mg/L |
| Total nitrogen | 100 mg/L | >50% removal; calculated outlet upper bound <50 mg/L |
| Trivalent chromium | 140 mg/L Cr³⁺ | >98% removal; calculated outlet upper bound <2.8 mg/L |
Treatment configuration
- Rough screening removed coarse material before pumping and mixing.
- Homogenisation evened out batch discharges from the tanning process.
- Chemical preparation and dosing used ferric chloride as coagulant, polyelectrolyte as flocculant and sodium hydroxide for pH control.
- Coagulation and flocculation tanks formed a separable floc before flotation.
- High-solids DAF clarifier separated both floated solids and settleable material.
- Sludge conditioning and filter pressing produced a reported 35% dry-solids cake.
What this case is useful for
The unusually useful part of this record is not simply the COD removal. It shows that a DAF can remove chromium efficiently only after pH correction and chemical precipitation have made it a particulate solid. It also shows the practical consequence of aggressive coagulation: significant primary sludge, which needs proper dewatering equipment and an approved disposal route.
For a tannery with similar wastewater, this is a credible starting reference for the treatment train and the expected primary-treatment role. It is not a replacement for jar testing, stream segregation and a discharge-specific design.
This page is based on a published supplier installation record. The plant identity and location have been withheld at the site owner’s request. The source states the flow, influent analysis, equipment sequence and removal performance, but does not publish independent laboratory certificates or a guaranteed outlet quality. Figures are a researched reference, not a performance warranty.